refactor: move model-specific args into model parsers (#1757)

examples/common/common.h

@@ -152,6 +152,7 @@ struct SDContextParams {
     std::string backend;
     std::string params_backend;
     std::string split_mode;
+    std::string model_args;
     bool auto_fit = false;
     std::string rpc_servers;
     std::string effective_backend;
@@ -165,12 +166,6 @@ struct SDContextParams {
     bool diffusion_conv_direct = false;
     bool vae_conv_direct       = false;
 
-    bool chroma_use_dit_mask = true;
-    bool chroma_use_t5_mask  = false;
-    int chroma_t5_mask_pad   = 1;
-
-    bool qwen_image_zero_cond_t = false;
-
     prediction_t prediction           = PREDICTION_COUNT;
     lora_apply_mode_t lora_apply_mode = LORA_APPLY_AUTO;